The present invention relates to fluid coupling devices of the type including both fluid operating chambers and fluid reservoir chambers, and valving which controls the quantity of fluid in the operating chamber.
Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine, and will be described in connection therewith. It is to be understood, however, that the present invention is not to be limited to use in fan cooling systems for automobiles and other vehicles, but has use in any cooling system for any engine.
Fluid coupling devices (“fan drives”) of the viscous shear type have become popular for driving engine cooling fans, primarily because their use results in substantial savings of engine horsepower. The typical fluid coupling device operates in the engaged, relatively higher speed condition only when cooling is needed, and operates in a disengaged, relatively lower speed condition when little or no cooling is required.
Today, electronically activated viscous fan drives are known and which can be precisely controlled between engaged, partially engaged and disengaged modes to control the output at a given fan speed as determined by the vehicle's engine computer.
For some time, one of the problems associated with fluid coupling devices used to drive radiator cooling fans was the phenomenon known as “morning sickness”. With these fluid coupling devices (fan drives), there was relatively little “drain back” or “bleed back”, i.e. a flow of fluid from the operating chamber back into the reservoir chamber when the engine was turned off and the fan drive ceased rotation. If a significant quantity of fluid was not bled back into the reservoir from the operating chamber, then when the operation of the fan would begin again after a long period of time (for example, the next morning), the fan drive would initially operate in the engaged condition for a period of time until most of the fluid in the operating chamber was pumped back into the reservoir. This existed even though the fan was cold and no cooling was required. Such engaged operation often resulted in an undesirable noise of the fan being driven when it was not required.
Several substantial improvements have been made with fluid coupling devices of the viscous shear type in order to overcome the problem of morning sickness. For example, in U.S. Pat. No. 6,752,251, a valve disk is provided which electronically controls movement of viscous fluid from the reservoir to the anti-bleed back chamber by energizing or deenergizing the actuator based on engine operating conditions.
One of the potential difficulties or concerns with some present fluid coupling devices of the viscous shear type is that the actuator could remain stuck in the engine “on”-electrically activated position, due to an improper flux pattern. In this situation, the fan could remain in operation when cooling is not needed. This could result in an overcooling situation and potentially create additional undesirable emissions from the vehicle engine.
It thus is an object of the present invention to provide an improved viscous shear fluid coupling device which eliminates morning sickness and at the same time minimizes or prevents improper freezing of the actuator member in an “on” position and thus minimizes or prevents the creating of additional undesirable emissions.